Generator control system



April 19, 1 R. M. CRITCHFIELD ET AL 2,467,963

GENERATOR CONTROL SYSTEM Fil ed Aug. 22, 1946 K ENVENTQRS y an h X 1Patented Apr. 19, 1949 GENERATOR CONTROL SYSTEM Robert M. Critchiieldand Paul L. Schneider, Anderson, Ind., assignorl to General MotorsCorporation, Detroit, Mich, a corporation of Delaware Application August22, 1946, Serial No. 692,351

3 Claims. 1

This invention relates to control means for a variable ratio drive to beused with automotive generators.

The power required to operate an automotive generator varies with speedand with electrical output, the latter depending on the electrical loadoperating in the vehicle and the state of charge of the battery. Whenconsidering the application of an electromagnetic or electro-hysteresiscoupling to the generator drive so that the required drive ratio can beobtained at low engine speeds to secure adequate generator output and sothat less drive ratio will be obtained at higher engine or car speeds inorder to reduce stress on rotating parts and to reduce wear,particularly that of brushes and commutators, some means for controllingthe slip of the coupling is necessary.

An object of the invention is to provide for the control of the slip ofan electrical coupling in such manner that the required generator outputwill be obtained at lower engine speeds while, in the higher speed rangeof the engine, the generator speed will not be excessive.

In the disclosed embodiment of the invention a speed actuated governoror other speed responsive means controls the energization of theelectromagnetic or electro-hysteresis coupling. The generator output maybe controlled by voltage and current regulators. A. governor driven bythe generator causes resistance to be added in the circuit of theexciting coil of the coupling when the speed of the generator tends tobecome excessive. As resistance is added, the slip of the couplingincreases thereby reducing the range of speed through which thegenerator is caused to operate by the engine whose speed range is muchgreater. The governor permits operation of the generator at a speed suchthat generator output will be slightly above the value for which thecurrent regulator is set.

Further objects and advantages of the present invention will be apparentfrom the following description, reference being hadto the accompanyingdrawing, wherein a preferred embodiment of the present invention isclearly shown.

In the drawing:

Fig. 1 includes a wiring diagram of the generator control system and alongitudinal sectional view of a suitable electrical coupling.

Fig. 2 is a sectional view on line 2-2 of Fig. 1.

Fig. 3 is a view of a punched sheet metal part used in the constructionof the coupling.

Fig. 4 is a fragmentary wiring diagram showing a modified form ofresistance control for use in the system shown in Fig. 1.

The electrical coupling will first be described with reference to Figs.1, 2 and 3. An engine driven shaft I is J'ournaled in bearings llsupported by a bracket l2. A key l3 connects shaft ID with a plate I 4connected by screws I5 with a magnetizable rotor I6 provided internallywith longitudinal slots, each of which receives a copper bar H. The barsll are all integral with side strips I8 and I3 which, when the bars areassembled with the rotor l6 as shown in Fig. 2, the side strips providerings and 2! respectively. Thus, the rotor l6 and the copper bars lljoined to the rings 20 and 2| provide a rotor of the squirrel cage type.

Shaft Ill supports roller bearings and ball bearings 26 supporting arotating field including a magnetizable tubular shaft 21 to which screws28 attach a plate 29 integral with shaft 30 which drives generator G. Asshown best in Fig. 2, the tubular shaft 21 provides diametricallyopposite pole pieces 3| each spanning, circumferentlally, slightly lessthan 90. Between pole pieces 3| are located pole pieces 32 (similar to3|) provided by a magnetizable plate 33 fitting against a shoulder 34provided by shaft 21 and maintained in that position by a nut 35threadedly engaging shaft 21 there being a spacer washer 36 between thenut and the plate. The shaft 21 and its pole pieces 3| and the plate 33with its pole pieces 32 embrace a field coil 40 whose leads 4| and 42are connected with slip rings 43 and 44 engaged respectively by brushes45 and 46. When the coil 40 is excited or energized, magnetism iscreated having a magnetic flux path which includes the shaft 21, plate33, the pole pieces 3| and 32 and the rotor I6. As the rotor l6 rotatesrelative to the pole pieces, eddy currents are generated in the bars I!and thereby creating a number of small magnetic circuits which try tocouple themselves with the magnetism produced by the coil 40. The lessthe excitation of the coil 40, the less will be the magnetic linkage andthe greater will be the slippage between the rotor l6 and the rotatingfield supported by shaft 21.

Below a certain speed of shaft Hi, the shaft l and the shaft aredirectly connected independently of the electrical coupling. For thispurpose, the rotor l6 supports pins each pivotally supporting a weightedlever 5|. A spring 52 urges each lever 5| toward the shaft and thus intoa notch 53 provided by the rotor l6 and into a notch 54 provided by aflange 55 extending from the shaft 21. The outer end of each spring isretained by a cup 56 integral with a shroud 51 supported by the plateII. The inter-engaging parts l6, 5| and 55 provide a. centrifugal clutchfor connecting the engine with the generator. The springs 52 may be suchas to maintain the clutch in engagement up to, for example, 4000 R. P.M. of the shaft Hi. When that speed is reached the weighted levers 5|fly out and disengage the shaft 30 from shaft l0. Above that speed, thegenerator speed is controlled by the magnetic coupling. when thecoupling is fully excited, it allows a certain slip, for example, 1000R. P. M., which is required in order to obtain the torque required fordriving the generator in order that it will continue to produce therequired output after the mechanical coupling is disengaged, althoughgenerator speed then falls to 3000 R. P. M., for example.

In order that the generator speed will not increase substantially beyondthat required to produce the required output, a governor 60 is providedfor regulating the current in the exciting coil 40 of the coupling. Thegovernor 60 comprises weights 6! attached by links 62 to plate 29 and bylinks 63 to a grooved collar 64. As speed increases weights 6| moveoutwardly by centrifugal force which is opposed by a. spring 6 laopposing left movement of collar 64 whose groove receives pins 65carried by the forks of a lever 66 pivoted at 61 and carrying a contact68 for engaging contact 69 of a spring blade 10 carrying a contact iifor engaging a contact 12 carried by a spring blade 74 carrying acontact 16 for engaging a contact ll carried by a spring blade 18carrying a' contact for engaging a contact 8! carried by a blade 82. Theblades l0, l4, l8 and 82 are attached respectively to supports 83, 84and 85 and 66. Resistance 81 bridges supports 83 and 84, resistance 88bridges supports 88 and 85 and resistance 89 bridges supports 85 and 80.Lever 66 is connected by wire 90 with ground. support 86 is connected bywire 9! with brush 46. Brush 85 is connected by ignition switch 92 withthe battery charging line to be described.

While the coupling members are mechanically connected up to 4000 R. P.M., for example, coupling field excitation is not required. At 4000 R.P. M., when the coupling is mechanically disconnected, full couplingexcitation is required. Therefore the coupling coil circuit should becompleted before shaft i0. attains4000 R. P. M. and should remaincompleted just after the coupling is mechanically disconnected when thegenerator speed drops to 3000 R. P. M. Consequently, the coupling coilcircuit should be completed at least at a speed of 3000 R. P. M. ofshaft ill before the coupling is mechanically disconnected. At about2800 R. P. M., the contact 68 engages a side contact 70a provided byblade 10. Therefore the circuit of coil 68 is completed althoughcontacts 68 and 59 may be separated. As the speed of shaft 30' increasesfrom 2800 up to 4000 R. P. M., while the coupling is mechanicallyconnected, the lever 66 moves counterclockwise successively to interruptthe short circuits of the resistances 81, 88 and 86. Just before thecou- 4 pling is mechanically disconnected, all three resistances areeifective to reduced coupling coil excitation. Immediately following themechanical disconnection of the coupling at 4000 R. P. M. of shaft 10,the spring 6la restores the lever to a position such that allresistances are short circuited and contact 68 is close to or touchingcontact 69. The speed of shaft 30 is then 3000 R. P. M. As engine speedincreases and the speed of shaft 30 tends to increase, notwithstandingthe slippage of the coupling when fully excited, lever 66 movescounterclockwise to cause blade 10 to move into a position such as shownin Fig. l to separate contacts II from I2 thereby interrupting the shortcircuit around resistance 81 and reducing the excitation of couplingcoil 60 so that the slippage will be greater. If engine speed is suchthat generator speed still tends to increase. the lever 66 will movestill further to cause blade 10 to bend further to the right and causeshook 13 to engage the blade 14 and bend it also to the right to separatecontact I6 from contact I1 thereby interrupting the short circuit of theresistance 88 further to decrease the excitation of the coupling coil40. If engine speed increases to the maximum and the generator speedstill tends to increase the movement of lever 66 still furthercounterclockwise, thereby causing hook 15 of blade 14 to engage lever 18to separate contact 80 from contact 8| whereupon the short circut ofresistance 89 is broken. The resistances 81, 88 and 89 are effective tolimit the excitation of coil 40. In this manner, the speed of thegenerator'is maintained within reasonable limits between 3000 and 4000R. P. M. for example. Instead of using a stepped resistance forcontrolling the excitation of coil 40, the lever 66 can be provided witha wiper 95 for engaging a rheostat 96. A wide contact 9'! engaged by thewiper 95 serves the purpose of contact 70a in Fig. l.

The regulation of current in the field winding F of the generator G iscontrolled by the voltage regulator i011 and current regulator H0. Theconnection between the generator G and the storage battery B is efiectedby reverse current or cutout relay 020.

Voltage regulator 70 comprises a generator voltage responsive windingH05 and a field current responsive winding i132 which surround a coreH03 cooperating with an armature E04 carried by a blade E05 fixed to agrounded support W6 and carrying a contact i0l for engaging a, contactI88 connected with a wire E09.

Current regulator comprises a generator output current responsive coiliii surrounding the core H2 cooperating with an armature H3 carried by aspring blade lid attached to a support H5 and carrying a contact H6engaging a contact lil connected by a wire H8 with coil E02 of thevoltage regulator.

The reverse current relay comprises a grounded voltage responsivewinding 4M and a current responsive winding Q22, the latter being in thebattery charging circuit. Windings Hi and I22 I surrounding a core E23cooperating with an armature 520 carried by a spring blade i25 attachedto a support B26 and carrying a contact 62? for engagement with thecontact :28 connected with the battery B and with the ignition switch 92by a wire 326. At a predetermined generator voltage the excitation ofthe coil 12H is sufficient to efiect the movement of armature i20 towardthe core l23 to efiect the completion of the battery charging circuit bythe engagement of contact i2ll and contact i28. Thereafter, generatorvoltage may fall below that value but the contacts will remain inengagement due to the magnetizing eflect of the coil I22. Therefore, solong as the generator voltage exceeds the battery voltage, the contactsI21 and I28 will remain in cm gagement. However, when generator speedfalls so low that the battery begins to discharge through the generator,the current in winding I22 is reversed and the contact I21 separatesfrom the contact I28.

Field winding F is connected with a terminal I30 connected with coil I02connected with resistance I3I which is connected with wire I09 andconnected with resistance I32 which is grounded. Before the regulators Iand III] begin to function, the field winding F is connected to groundthrough the contacts of the current regulator and the contacts of thevoltage regulator. When the voltage of the generator attains the valuefor which the voltage regulator is set,

the contact I01 separates from the contact I08 thereby renderingresistance I32 operative to limit the field current. When the currentoutput of the generator exceeds that for which the current regulator isset, contact II6 separates from contact In and resistances I3I and I32are both effective to limit the field current. During the lower speedrange of the engine, while the coupling parts are mechanicallyconnected, the generator speed is high relative to engine speed and thecutout relay closes at a relatively low engine speed to connect thegenerator with the battery. As engine speed increases, the regulatorsbecome effective to limit the voltage and output of the generator. diumvalue, the coupling members are mechanically disconnected and thereafteras engine speed increases, coupling slip is controlled in a manner suchthat generator speed will not become excessive but the speed will besufficient to provide generator voltage and current output for which theregulators are set.

In some installations, it may not be necessary to use the speedresponsive mechanical connection between the coupling members. If thelevers I are omitted, the maximum excitation of the coupling coil 50would remain in effect until the generator speed begins to exceed thatrequired for the voltage current output for which the regulators areset. This effect can be obtained by using a spring 5Ia of suitablecalibration and by the proper initial separation of the contacts 68 fromthe contacts '59 so that contact 1| does not separate from contact I2until the generator speed begins to rise above that which is requiredfor the desired voltage and current output. The contact a of Fig. 1 andthe contact 9! of Fig. 4 should have such length that, at zero speed,they would be engaged by contact 58 and wiper 95, respectively.

When the voltage regulator starts operating, the generator tends to runfaster because its output and torque requirements are limited by thevoltage regulator. As the generator speed tends to exceed that for whichthe governor is set to operate, the excitation of coil of the rotatingfield of the coupling is reduced by the governor 60 so that the requiredgenerator speed is maintained.

While the embodiment of the present invention as herein disclosed,constitutes a preferred form, it is to be understood that other formsmight be adapted, all coming within the scope of the claims whichfollow.

When engine speed attains a me- What is claimed is as follows:

1. A generator control system for use on automotive vehicles in whichthe propelling engine drives a generator comprising, in combination, atransmission between the engine and the generator including anelectromagnetic coupling having an exciting coil and providing slipvarying with the current in the coil, means for mechanically connectingthe engine and generator independently of the electromagnetic couplingand operating in response to the attainment of a certain engine speed todisconnect mechanically the generator and engine leaving the couplingeffective to transmit torque from the engine to the generator, saidcoupling when fully excited providing a certain slip whereby, when themechanical connection is interrupted, generator speed decreases to avalue less than when driven by the engine through the mechanicalconnection just before interruption thereof, and means which operates topermit full excitation of the coupling at the speed value to which thegenerator speed falls when the mechanical connection is interrupted andoperating thereafter to reduce the excitation of the coupling coil asgenerator speed tends to increase above the speed last mentioned.

2. In a generator control system for use on an automotive vehicle havinga propelling engine to drive a generator, a transmission mechanism0perable to provide a drive between the engine and the generator, saidmechanism including an electromagnetic coupling having an exciting coiland providing a slip varying with the current in the coil; centrifugalmeans for mechanically connecting the engine and the generatorindependently of the electromagnetic coupling and operating in responseto the attainment of a certain engine speed to disconnect mechanicallythe generator and engine leaving the coupling effective to transmittorque from the engine to the generator; a circuit between the field ofthe generator and the coil for regulating the current in the excitingcoil; a resistance in the circuit; speed responsive means rotatable withthe shaft of the generator for controlling the resistance, said meansincreasing the resistance up to the time the coupling is mechanicallyconnected to limit the excitation of the coil so that when themechanical connection is interrupted the generator speed decreases to avalue less than when driven by the engine through the mechanicalconnection, said speed responsive means controlling the resistance afterthe mechanical interruption according to the speed of the generator.

3. In an apparatus of the class described the combination comprising, adriving member, a driven generator, an electromagnetic coupling betweenthe member and the generator having an exciting coil and providing aslip varying with the current in the coil; an electric circuit betweenthe field of the generator and the coil for controlling the output ofthe generator; a plurality of resistance units in the circuit; shuntsfor the resistance units; means for mechanically connecting the drivingmember and generator independently of the coupling and operating inresponse to the attainment of a certain speed of the driving member todisconnect mechanically the driving member and the generator leaving thecoupling effective to transmit torque from the driving member to thegenerator; speed responsive means rotatable with the generator andoperative to close the circuit to excite the coil of the coupling andadapted gradually to cut in said resistance units by cutting out theshunts accuses with increase of speed or the generator, said REFERENCEScoupling when fully excited providing slip The following references areo2 record in the whereby, when the mechanical connection is in--terrupted, generator speed decreases to a value me of this patent lessthan when driven by the driving member 5 I I STA PATENTB through themechanical connection just before Number Name mm the interruptionthereof, said. speed responsive A means operating, after the mechanicalconnection is interrupted to shunt out the resistance as the speed ofthe generator is reduced and vice W Y F RHGN ll .3

verse Number Gountry Date ROBERT CmmmELD- $66,978 France Mar, 2Q, 19%

PAUL L. SC 1min;

